1. Field of the Invention
The present invention relates to an enclosed kneading apparatus for kneading materials such as rubber, plastic and so forth by rotating rotors in a chamber.
2. Description of the Related Art
Batch-type enclosed kneading apparatuses manufacture a batch of kneaded products by a series of operations such that kneading materials such as rubber, plastic and so forth are pressed into a chamber by a floating weight, the materials are kneaded by a pair of rotors provided in the chamber to obtain a kneaded product of a desired state, and the kneaded product is discharged from the chamber through a drop door.
The above kneading is performed by allowing a rotation force of the rotors to act as a shearing force on the kneaded product. It has been known that the shearing force is maximum in a clearance between the rotors and the inner wall of the chamber (hereinafter, referred to as tip clearance), and the maximum shearing force increases with the decrease of the tip clearance. Therefore, it is apparent that decreasing the tip clearance accelerates the kneading due to the dispersive action caused by a large shearing force. However, if the tip clearance decreases, a large shearing force is locally imparted to the kneaded product, so that the temperature of the kneaded product increases.
Thus, in the case of manufacturing a kneaded product having a low allowable temperature, steps are taken such that the tip clearance is set to increase, the rotor speed is decreased although productivity decreases, and the input amount of materials is reduced in order to prevent an increase in the temperature over the allowable temperature even if kneading efficiency is low. In addition, in the case of manufacturing a kneaded product having a high allowable temperature, the tip clearance is sufficiently decreased and the rotor speed is increased in order to obtain a large shearing force while attaching importance to kneading efficiency.
According to the above conventional arrangements, however, the tip clearance is suitable only for a specific kneading condition. Thus, unless the rotors are replaced so as to provide a tip clearance responsive to the kneading condition when the type of the kneaded product is switched to change the kneading condition, an excessive tip clearance or a too small tip clearance is provided which exacerbates the problems of insufficient kneading and dispersion, and the increase in temperature of the kneaded product over the allowable temperature. However, it is impractical to replace the rotors in response to the kneading condition. When the temperature of the kneaded product increases over the allowable temperature, the quality of the kneaded product is actually ensured at the sacrifice of the handling capacity of the kneading apparatus, i.e., by decreasing the speed of rotors and reducing the input amount of materials.
When merely increasing the cooling efficiency, an enclosed kneading apparatus as disclosed in Japanese Unexamined Patent Publication No. 63-47106 may be used in which two helical long wings extending in the axial direction are provided in the circumferential direction, scrapers are disposed at the back of the long wings, and a kneaded product layer attached to the inner surface of a chamber is scraped off by the scrapers, whereby the cooling efficiency through the chamber is increased. In the above enclosed kneading apparatus, however, only the long wings provide a specific tip clearance and perform a shearing function, and the technical idea of imparting the shearing function to the scrapers is not described, so that the apparatus is insufficient in the sense of a change of the tip clearance.
In addition, an enclosed kneading apparatus has been developed in which rotation axes of rotors can move so that the tip clearance can be arbitrarily changed in response to the kneading condition rather than impractical replacement of the rotors. In this case, however, checking and maintenance of a mechanism for moving the rotation axes of the rotors are required each time the axes are moved, the setup time increases, and the checking operation becomes complicated.